International Space Station

The ISS remains in orbit because it travels sideways around Earth fast enough that, while gravity continuously pulls it downward, Earth's curved surface falls away beneath it. Using the TransitSatellite catalog altitude of approximately 416 km (259 mi) as an idealized circular orbit, its estimated speed is 7.66 km/s, 27,574 km/h, or about 17,134 mph.

The ISS remains in orbit because it travels sideways around Earth fast enough that, while gravity continuously pulls it downward, Earth's curved surface falls away beneath it. Using the TransitSatellite catalog altitude of approximately 416 km (259 mi) as an idealized circular orbit, its estimated speed is 7.66 km/s, 27,574 km/h, or about 17,134 mph.

At that representative altitude, one orbit takes approximately 92.9 minutes. That equals about 15.5 orbits per day, with an estimated orbital circumference of approximately 42,689 km (26,526 mi). The station's real altitude, speed and orbital period change as atmospheric drag, reboost maneuvers, visiting spacecraft and other perturbations affect its orbit.

Microgravity does not mean that gravity has disappeared. The ISS and everything inside it are falling together around Earth, creating continuous free fall. This environment allows researchers to study processes such as fluid behavior, combustion, crystal growth, plant development, materials and changes to the human body with greatly reduced effects from weight.

Constructing and operating the ISS requires orbital rendezvous, docking, attitude control, electrical-power management, thermal control, communications, life support, robotics and repeated cargo and crew missions. Spacecraft approaching the station must carefully match its orbital plane, altitude, timing and relative velocity before docking.

Objects in this category may be crewed stations, modules, cargo vehicles, or other spacecraft directly connected with human activity in orbit. The exact role depends on the individual object.

• The ISS remains in orbit because it travels sideways around Earth fast enough that, while gravity continuously pulls it downward, Earth's curved surface falls away beneath it. Using the TransitSatellite catalog altitude of approximately 416 km (259 mi) as an idealized circular orbit, its estimated speed is 7.66 km/s, 27,574 km/h, or about 17,134 mph.
• At that representative altitude, one orbit takes approximately 92.9 minutes. That equals about 15.5 orbits per day, with an estimated orbital circumference of approximately 42,689 km (26,526 mi). The station's real altitude, speed and orbital period change as atmospheric drag, reboost maneuvers, visiting spacecraft and other perturbations affect its orbit.
• Microgravity does not mean that gravity has disappeared. The ISS and everything inside it are falling together around Earth, creating continuous free fall. This environment allows researchers to study processes such as fluid behavior, combustion, crystal growth, plant development, materials and changes to the human body with greatly reduced effects from weight.
• Constructing and operating the ISS requires orbital rendezvous, docking, attitude control, electrical-power management, thermal control, communications, life support, robotics and repeated cargo and crew missions. Spacecraft approaching the station must carefully match its orbital plane, altitude, timing and relative velocity before docking.

The ISS remains in orbit because it travels sideways around Earth fast enough that, while gravity continuously pulls it downward, Earth's curved surface falls away beneath it. Using the TransitSatellite catalog altitude of approximately 416 km (259 mi) as an idealized circular orbit, its estimated speed is 7.66 km/s, 27,574 km/h, or about 17,134 mph. At that representative altitude, one orbit takes approximately 92.9 minutes. That equals about 15.5 orbits per day, with an estimated orbital circumference of approximately 42,689 km (26,526 mi). The station's real altitude, speed and orbital period change as atmospheric drag, reboost maneuvers, visiting spacecraft and other perturbations affect its orbit. Microgravity does not mean that gravity has disappeared. The ISS and everything inside it are falling together around Earth, creating continuous free fall. This environment allows researchers to study processes such as fluid behavior, combustion, crystal growth, plant development, materials and changes to the human body with greatly reduced effects from weight. Constructing and operating the ISS requires orbital rendezvous, docking, attitude control, electrical-power management, thermal control, communications, life support, robotics and repeated cargo and crew missions. Spacecraft approaching the station must carefully match its orbital plane, altitude, timing and relative velocity before docking.

The current two-line element set reports approximately 15.4918 revolutions per day. Dividing 1,440 minutes by that value gives an estimated orbital period of 93 minutes.

ISS assembly began when the Russian-built Zarya control module launched aboard a Proton-K rocket from Baikonur Cosmodrome on 20 November 1998. The Unity connecting module followed aboard Space Shuttle Endeavour in December 1998. The first long-duration residents—Expedition 1—arrived in November 2000. The station was assembled through dozens of missions carrying laboratories, habitation modules, trusses, solar arrays, robotic systems and other equipment. Its launch story is therefore not one launch but an international construction campaign conducted in orbit over many years.

Low Earth orbit is the region closest to Earth used by most crewed spacecraft, many science missions, Earth-observation satellites, and large constellations. Objects move quickly and commonly complete an orbit in roughly 90 to 130 minutes.

LEO can provide detailed Earth views, lower communications delay, and easier access than higher orbits, but it covers less area per spacecraft and is more affected by atmospheric drag.

• Why do low-orbiting stations circle Earth many times per day?
• How do crews receive power, supplies, and communications in orbit?

Current identity and orbital elements come from CelesTrak’s public GP data. Calculated orbit values are derived from the current TLE and may change after catalog updates. Mission-history claims are added separately and require authoritative sources.

• CelesTrak NORAD GP Element Sets
• International Space Station Facts and Figures · NASA
• 25 Years Ago: NASA, Partners Begin Space Station Assembly · NASA
• Station Science 101: Research in Microgravity—Higher, Faster, Longer · NASA